1. Field of the Invention
The present invention relates to internal combustion engines and like apparatus which includes a mechanism for converting the reciprocating motion of one or more pistons into rotational motion of an output element, and in which the motion converting mechanism emulates an elliptic trammel type or "ellipsograph" linkage.
2. Description of the Prior Art
As is well known, conventional internal combustion engines utilize piston rod and crank mechanisms for converting the reciprocating motion of the pistons into rotational motion of an output shaft. Such conventional mechanisms have certain drawbacks. For example, the piston and cylinder wall surfaces wear substantially as a result of side thrust forces. These side forces may also cause significant power losses due to friction. Piston/cylinder mismatches may also cause jamming of the pistons. Moreover, these conventional engines often lack appropriate balancing means, so that non-balanced, secondary inertial forces constrain the angular velocity of the output shaft thereby limiting increases in power output. Still further, conventional crankshafts tend to be massive, reflecting the strength that is built into them in order to handle full output torque. Durability is sometimes compromised because of insufficient lubrication of the pistons working in a high-temperature environment.
A known alternative to the conventional piston rod and crank internal combustion engine (ICE) utilizes an elliptic trammel linkage, or "ellipsograph" mechanism for converting the reciprocating motion of the pistons into rotational motion of an output shaft. An improved version of an ICE incorporating such a mechanism is disclosed in U.S. Pat. No. 5,189,994 issued Mar. 2, 1993 and incorporated herein by reference. FIG. 1 of the prior art '994 patent, which figure has been reproduced as FIG. 1 herein, shows a two-dimensional schematic representation of an engine 10 employing the "ellipsograph" principle. The engine 10 includes an engine block or casing 12 carrying a crankshaft bearing 14. The casing 12 defines a horizontal cylinder 16 and a vertical cylinder 18 disposed orthogonally relative to each other along an X axis and a Y axis, respectively. The cylinders 16 and 18 are provided with intake and exhaust valves 19. Pistons 20 and 22 are received for reciprocation within the cylinders 16 and 18, respectively. A connecting rod 24 couples the piston 20 with a horizontal guide in the form of a slide 26 movable within a linear guideway 28 aligned with the X axis; similarly, a connecting rod 30 couples the piston 22 with a vertical guide in the form of a slide 32 movable within a linear guideway 34 disposed along the Y axis. A link or orbital crankshaft 36 connects the slides 26 and 32 at end points 38 and 40. Last, a power output crank 42 having one end connected to the midpoint 44 of the orbital crankshaft 36 and its other end journaled in the bearing 14, is rotatable about a central point 46 lying on a longitudinal Z axis mutually orthogonal to the X and Y axes. It will be evident that the two-dimensional mechanism of FIG. 1 is theoretical only; for example, the intersecting guideways 28 and 34 would preclude realization of a practical engine which would require that the guideways be offset along the Z axis.
In the operation of the engine shown schematically in prior art FIG. 1, as the pistons 20 and 22 reciprocate in their respective cylinders and with the pistons alternately reaching their top and bottom dead centers, the ends 38 and 40 of the orbital crankshaft reciprocate between their horizontal and vertical endpoints equidistant from the Z axis represented by the point 46. The output crank 42 is thereby driven with an angular velocity, .omega., with the point 44 describing a circle centered on the Z axis. At the same time, the orthogonally disposed, linear slides and guides together with the crank 42, constrain the orbital crankshaft 36 to counterrotate at an angular velocity of -.omega. about an axis passing through the point 44.
As explained in the '994 patent, IC engines employing the principles of that patent have significant advantages. Nevertheless, the slide/guide arrangement disclosed in the '994 patent has been found to have several drawbacks. For example:
(a) the alignment requirements imposed by the slide/guide arrangement result in difficulties in packaging the engine crankcase; PA1 (b) significant side loads produced within the slide-guide mechanisms result in friction losses, especially at high rpm, approaching those encountered in conventional piston/crank IC engines; PA1 (c) pressurized lubrication of the slide/guide arrangement requires a high capacity, high pressure oil pump that is costly and consumes substantial power and it is moreover difficult to retain sufficient oil within the fast moving slide/guide mechanism to adequately lubricate that mechanism; and PA1 (d) the mass of the reciprocating slide-guide mechanisms is substantial and precludes reducing the total mass of the moving parts to below that of conventional IC engines.
Thus, although relatively slow, large engines such as those used for marine applications may successfully use the principles of the '994 patent, the foregoing drawbacks render ICEs employing the slide/guide arrangement of the '994 patent uncompetitive with present high rpm conventional engines used, for example, to power passenger vehicles.
Accordingly, it is an overall object of the present invention to provide an ICE or like apparatus that eliminates dependency on the slide/guide arrangement of known elliptic trammel type linkages while preserving the benefits of such mechanisms.